1. Field of the Invention
The present invention relates to a probing system of vascular endothelium functions, particularly relates to a probing method where a positioning operation with the aid of a robot arm and an image processing operation are combined.
2. Brief Description of the Related Art
Arterial scleroses, a main cause of a cerebrovascular disease infarction and a myocardial infarction among three major causes of death in the Japanese, have been increasing as diets of the Japanese have been westernized. Consequently, noninvasive and simple probing methods to detect such arterial scleroses at their early stages, have been required.
An Examination method of a vascular endothelium function is used as one of such examination methods. In this method, a function of the vascular endothelium (i.e. inner most cell layers of a vascular wall which regulate vasodilation/vasoconstriction by releasing a vasodilator) is measured. In an examination procedure of the vascular endothelium function, after a blood vessel diameter at rest is determined, a lower portion of the arm is avascularized for 5 minutes by applying 250 mmHg of pressure with a cuff around the arm and released so as to generate a vascular dilating reaction caused by blood flow. An increased rate of a blood vessel diameter due to flow mediated vasodilation against the blood vessel diameter at rest is used as an index to evaluate arterial sclerosis. Hashimoto et al. reported in a Japanese medical journal (Rinsho-i (1998): 24(5) pp789-791) that a dilated degree in a subject with a slight arterial sclerosis is ca. 10% while a dilated degree in a subject with a grave arterial sclerosis is lowered to ca. 2%.
They determined blood vessel diameters in such a manner that after an ultrasound probe was applied to an arm of a subject and a appropriate blood vessel image along its longitudinal direction is acquired and stored for determining blood vessel diameters. They recognized the blood vessel walls in the acquired image by their naked eyes and the blood vessel diameters are determined based on the recognized walls.
Fan et al. determined the blood vessel diameters by processing images acquired by medical doctors (IEEE Transaction on Medical Imaging: Vol. 19, No. 16, June 2000, pp621-631).
However, in the method by Hashimoto et al., it takes a fairly long time to acquire images and reproducibility of the determined blood vessel diameters is poor because walls are recognized by naked eyes. Further, it is reported that in the method by Fan et al. determined results largely depend on images even when images are selected from the same subject.
The present invention is carried out to solve the problems mentioned above and to provide an examination method of the vascular endothelium function by combining a positioning operation with the aid of a robot arm and an image processing operation. The present invention attains a more rapid examination method with improved reproducibility when determining blood vessel diameters.
More specifically, the present invention having the following arrangements (1) to (9) solve the problems mentioned above.
(1) A method of examining a vascular endothelium function by an automatic measurement system comprising: a measuring system comprising an ultrasound diagnostic device and an ultrasound probe attached to the ultrasound diagnostic device for acquiring an ultrasound image; an image processing and calculating system comprising a computer and an image processing board for processing the acquired ultrasound image by the measuring system; and a navigation system comprising a robot arm for moving and rotating the ultrasound probe, wherein the method comprises steps of: a first step wherein an ultrasound image is acquired after the ultrasound probe is moved to a subject portion for probing its vascular endothelium function and the acquired image is processed for calculating and controlling a position of the ultrasound probe so that the center of a blood vessel to be probed is laid on the center of the image; a second step wherein a series of operations comprising an operation for acquiring ultrasound image, an operation for processing and calculating the acquired ultrasound image and an operation for moving the robot arm based on the calculated result, are repeated starting from the finally acquired ultrasound image at the first step so that the ultrasound probe is moved to in a parallel position to the center line of the blood vessel; a third step wherein a series of operations comprising an operation for acquiring ultrasound image, an operation for processing and calculating the acquired ultrasound image and an operation for moving the robot arm based on the calculated result, are repeated starting from the finally acquired ultrasound image at the second step so that the ultrasound probe is moved to a position where the ultrasound probe is in parallel to and immediately above the center line of the blood vessel; and a fourth step wherein a blood vessel diameter is determined from the finally acquired ultrasound image at the third step.
(2) The method according to (1), wherein: the center of gravity of a color Doppler signal area in the acquired ultrasound image is recognized as the center of the blood vessel.
(3) The method according to (1), wherein: a distance between two boundaries determined such that a certain width along X-axis of the acquired ultrasound image is extracted, in the extracted width gradient of image energy defined as accumulated brightness in the perpendicular direction to the X-axis, is examined and two maximum point in the gradient are determined as the boundaries and the determined distance is determined as the blood vessel diameter.
(4) The method according to (1), wherein: the robot arm is controlled by two moving degrees of freedom and one rotating degree of freedom.
(5) The method according to (1), wherein: the robot arm is moved and controlled along the X-axis direction in the first step.
(6) The method according to (1), wherein: the robot arm is rotated and controlled around the Z-axis in the second step.
(7) The method according to (1), wherein: the robot arm is moved and controlled along the X-axis direction in the third step.
(8) The method according to (1), wherein the second and the steps respectively further comprise steps of: any one of the ultrasound images acquired during a series of operations is divided by a predetermined width in the X-axis direction into a plurality of segments; a blood vessel diameter in each divided segment is determined; a median value is selected among determined blood vessel diameters; the number of determined blood vessel diameters which fall into a certain range centered by the median value, is calculated; a score value is calculated by dividing the calculated number by the total number of the divided segments; score values calculated from respective series of acquired ultrasound images are compared; and a position having a maximum score value is judged as an optimum position of the ultrasound probe in the second step or the third step.
(9) The method according to (1), wherein: a changing passage after the blood vessel is dilated, is tracked on a real-time basis.